Packing materials for liquid chromatography (LC) are generally classified into two types: organic materials, e.g., polydivinylbenzene, and inorganic materials typified by silica. Many organic materials are chemically stable against strongly alkaline and strongly acidic mobile phases, allowing flexibility in the choice of mobile phase pH. However, organic chromatographic materials generally result in columns with low efficiency, particularly with low molecular-weight analytes. Many organic chromatographic materials not only lack the mechanical strength of typical chromatographic silica but also shrink and swell when the composition of the mobile phase is changed.
Silica is the material most widely used in High Performance Liquid Chromatography (HPLC), Ultra Performance Liquid Chromatography (UPLC), and Supercritical Fluid Chromatography (SFC). The most common applications employ silica that has been surface-derivatized with an organic functional group such as octadecyl (C18), octyl (C8), phenyl, amino, cyano, etc. As stationary phases for HPLC, these packing materials result in columns that have high efficiency and do not show evidence of shrinking or swelling.
Current Hybrid Material Technologies (HMT) provide important solutions to traditional chromatographic problems experienced with silica-based packing materials. HMT improvements include dramatically improved high and excellent low pH stability, great mechanical stability, good peak shape when used at pH 7, high efficiency, good retentivity, and desirable chromatographic selectivity.
However, two problems have been noted for some HMT and silica materials. The first is poor peak shape for bases when used at low pH and low ionic strength, which can negatively impact loadability and peak capacity when used at low pHunder these conditions.
A second problem observed for many HMT and silica materials is a change in acidic and basic analyte retention times (denoted ‘drift’) after a column is exposed to repeated changes in mobile phase pH (e.g., switching repeatedly from pH 10 to 3).
Thus, there remains a need for alternative materials that provide superior peak shape and reduced drift.